It's not dead, there are servers that have players in them at any given time. Already seen most servers mentioned here but others like the -[EVIL]- servers that are hosted in the USA usually have players in them and if you like to jump around, SkillzWorld has a popular climb server and other European-based servers where you can conc and rocket jump etc. Hell even if you like to co-op against bots, Bot Busters Crematorium always has players.